An IC (integrated circuit) die typically is housed within an IC (integrated circuit) package having leads that are coupled to conductive pads on the IC die for providing connection to nodes of the integrated circuit. Referring to FIG. 1, a cross sectional view of a lead frame strip 100 of an IC package includes an IC die 102 mounted on a die frame dap 104. The die frame dap 104 is coupled to the lead frame strip 100 via tie bars 108. The structures of the lead frame strip 100 are part of an IC package and are known to one of ordinary skill in the art of IC package manufacture.
Further referring to FIG. 1, a lead interconnect 112 of the lead frame strip 100 is coupled to a conductive pad on the IC die 102 for providing connection to a node of the integrated circuit of the IC die 102. A conductive ball 114 is bonded to a conductive pad 116 on the IC die 102. The conductive ball 114 is coupled to the lead interconnect 112 via a wire 118. FIG. 1 is a cross sectional view along a line A--A of a top view of the lead frame strip 100 of FIG. 2.
The performance of the integrated circuit of the IC die 102 is determined by the quality of bonding between the conductive ball 114 and the conductive pad 116. Referring to FIG. 3A, the conductive ball 114 is bonded to the conductive pad 116 using an ultrasonic and heating process to form an intermediary material 120 that bonds the conductive ball 114 to the conductive pad 116, as known to one of ordinary skill in the art of IC package manufacture. In the ultrasonic and heating process, the intermediary material 120 is formed from a first conductive material of the conductive ball 114 and a second conductive material of the conductive pad 116. For example, if the conductive ball 114 is comprised of gold and the conductive pad 116 is comprised of aluminum, then the intermediary material 120 is comprised of an intermetallic alloy (Au.sub.x Al.sub.y) formed from the gold of the gold ball 114 and the aluminum of the aluminum pad 116.
FIG. 3A illustrates an example of poor bonding between the conductive ball 114 and the conductive pad 116. In FIG. 3A, a relatively low amount of material of the conductive ball 114 and the conductive pad 116 have been used to form a low amount of the intermediary material 120. With such low amount of intermediary material 120 bonding the conductive ball 114 to the conductive pad 116, the conductive ball 114 may have high resistance poor contact with the conductive pad 116. Such high resistance degrades the speed performance of the integrated circuit within the IC die 102.
FIG. 3B illustrates an example of good bonding between the conductive ball 114 and the conductive pad 116. In FIG. 3B, a relatively high amount of material of the conductive ball 114 and the conductive pad 116 have been used to form a high amount of the intermediary material 120. With such high amount of intermediary material 120 bonding the conductive ball 114 to the conductive pad 116, the conductive ball 114 may have low resistance good contact with the conductive pad 116. Such low resistance enhances the speed performance of the integrated circuit within the IC die 102.
Because the performance of the integrated circuit within the IC die 102 depends on the quality of bonding between the conductive ball 114 with the conductive pad 116, the quality of bonding is monitored during manufacture of IC packages. Referring to FIG. 4A, in the prior art, a cross section along line B--B is made to result in the cross sectional view of FIG. 4B of the intermediary material 120 between the conductive ball 114 and the conductive pad 116. Such a cross sectional view is analyzed to determine the quality of bonding between the conductive ball 114 and the conductive pad 116. For example, a resin material is formed around the conductive ball 114 and the conductive pad 116, and the conductive ball 114 and the conductive pad 116 are polished from the side inward to the cross section B--B to result in the cross sectional view of FIG. 4B.
For consistent analysis, the cross section B-B should consistently be through the center of the conductive ball 114 as multiple IC packages are examined. However, polishing down to the exact center of the conductive ball 114 in the prior art is difficult to control. Referring to FIG. 5A, if the cross section B--B is not at the center of the conductive ball 114, then the cross sectional view of FIG. 5B results with an inaccurate representation of the amount of intermediary material 120 between the conductive ball 114 and the conductive pad 116. Thus, the quality of the bonding between the conductive ball 114 and the conductive pad 116 cannot be consistently determined with the polishing method of the prior art.
In addition, a cross section of the intermediary material 120 may not be an accurate representation of the quality of bonding between the conductive ball 114 and the conductive pad 116. For example, if a void or a contaminant is present within the intermediary material 120, and if the cross section is not through such a void or contaminant, then the cross section alone may not represent the poor contact between the contact ball 114 and the contact pad 116 from such a void or contaminant.
Nevertheless, because bonding between the conductive ball 114 and the conductive pad 116 in an IC package determines the performance of the integrated circuit, accurate and consistent determination of the quality of bonding is desired.